1. Field of the Invention
The present invention relates to a method for manufacturing a solid-state imaging device and to the solid-state imaging device and, more particularly, to a treatment of the shape of a condensing lens for the solid-state imaging device.
2. Description of the Related Art
The solid-state imaging device using a CCD or an imaging device such as an area sensor is basically constituted to include a photoelectric conversion portion such as a photodiode, and a charge transfer portion having a plurality of charge transfer electrodes for transferring electric charges read out from the photoelectric conversion portion. The charge transfer electrodes are arranged adjacent to each other over a charge transfer channel formed on the surface of a semiconductor substrate, and are sequentially driven with a clock signal.
In recent years, the solid-state imaging device is made more and more miniaturized in its pixels by reducing its size and by increasing the number of imaging pixels. Accordingly, the miniaturization of the photoelectric conversion portion advances to make it difficult to keep the sensitivity high. In order to improve the sensitivity, therefore, there have been proposed a variety of constitutions (e.g., JP-A-9-45884) for enhancing the condensation efficiency on the photodiode by mounting a micro-lens on the surface of the pixel.
As one of them, as shown in FIG. 10, there has been proposed a constitution, in which a passivation film 20 is formed on a flattened layer 10 just above a photodiode portion 30 constituting the photoelectric conversion portion, in which an in-layer lens 21 is formed over the passivation film 20 and in which a flattened film 22, a color filter 50, a flattened film 70 and an on-chip lens 60 are formed over the in-layer lens 21 are formed sequentially in the recited order (although a charge transfer portion 40 and the photodiode portion 30 will be described herein after in connection with embodiments).
In the solid-state imaging device of the related art thus far described, both the two condensing lenses of the in-layer lens and the on-chip lens are formed by forming and transferring resist patterns. For example, the in-layer lens is manufactured in the following manner.
In this method, the photodiode portion, the charge transfer portion and the flattened film are formed at first. After this, a silicon nitride film to become the lens substrate 21 is formed, as schematically shown in FIG. 11A. A resist pattern R1 is formed over the silicon nitride film and is caused to reflow and set thereby to acquire a desired curvature (FIG. 11B). An anisotropic etching is performed by using that resist pattern R1 as a mask thereby to transfer the surface shape of the resist pattern R1 to the lens substrate made of the silicon nitride, so that the in-layer lens having the same curvature as that of the resist pattern R1 is formed (FIG. 11C).
In the method of the related art, as described hereinbefore, the shape obtained by the reflow of the resist pattern R1 becomes, as it is, the curvature of the condensing lens. The method has a problem that the curvature is so seriously changed by changing the reflow temperature as to make the curvature control extremely difficult.